The operations of blockchain also incur costs in terms of latency and energy consumption [1]}. In fact, the execution of blockchain mining tasks, e.g., block verification and information exchange among miners requires large energy sources to be consumed. To be clear, in order to append a new transaction to the blockchain, a blockchain user or a miner needs to run a mining puzzle, e.g., PoW which is generally complicated and requires vast computing and storage resources. This issue becomes more important in the mobile blockchain network where mobile devices often have limited battery and memory which make them challenging to accommodate all mining tasks. Moreover, the repeated information exchange among miners in the mining group also requires large bandwidth resources and results in high communication latencies which potentially degrades the overall performance of FLchain training, e.g., delayed model aggregation. Therefore, it is highly important to carefully consider latency and energy aspects to minimize possible costs caused by the blockchain adoption in FLchain systems.
